In a cooking appliance such as, for example, an induction heating appliance for cooking, a housing, in which a plurality of heaters or induction heating coils, an inverter circuit and a control device for the inverter circuit are accommodated, has its top provided with a top plate made of a heat resistant glass. A cooking container to be heated is generally placed atop the top plate in alignment with a heating region indicatively marked by, for example, a circle depicted on the top plate. In the standard induction heating appliance, the heating region is generally employed three in number, with three heating regions defined at respective predetermined positions each indicated by the circle, so that three cooking containers can be simultaneously heated for cooking. Various operating elements for the induction heating appliance that are to be manipulated by the user one at a time, including, for example, electric power switches, adjustment knobs for adjusting heating capacities and indicator lamps and labels, are integrated on an operating panel. In some models now available in the market, the operating panel is of a fixed type, i.e., a type fixed to a portion of a front surface of the housing, which is perpendicular to the top plate. The operating panel of the fixed type lies perpendicular to the top plate and is positioned below the top plate and, therefore, when the user desires to operate one or some of those operating elements and/or to ascertain statuses of indicators and/or labels, the user is required to bend his or her upper body down and look at the operating panel. For this reason, the prior art cooking appliance has a problem associated with operability of such appliance.
As an improved version of the fixed type operating panel referred to above, a rotary container type of the operating panel has been made available, in which the operating panel is accommodated in a rotatable compact box and the latter is in turn mounted on a front portion of the housing. Since this rotary container type operating panel is, when in use, pulled to pivot forwards and is, when not in use, concealed deep within the housing, such operating panel is appealing in that it will not provide an obstruction to the user when accommodated within the housing. However, when in use, the rotary container type may occasionally provide an obstruction to the user as the operating panel remains pulled to pivot forward. In view of this, some users come to be accustomed to using the operating panel of the rotary container type in such a way that only when access to the operating panel is needed during cooking, he or she pulls the rotary container to pivot forward in readiness for manipulation of one or some of the operating elements, but when such access is no longer necessary, he or she pushes the rotary container to pivot backwards to allow it to be completely accommodated within the housing. This is indeed tiresome to handle and even this rotary container type similarly has a problem associated with operability.
In an attempt to alleviate the foregoing problems, the cooking appliance of a similar kind comfortable to handle has been disclosed, in which the operating switches and indicators are disposed in an endwise region of the top plate close to the user (which region is hereinafter referred to as a foreside of the top plate) together with a backlighting unit so that when those operating elements are in a condition ready to be operated, the backlighting unit can be activated to illuminate a periphery of those operating elements to provide the user with an indication of “Readily Available for Operation” (see, for example, Japanese Laid-Open Patent Publication No. 2003-272816).
According to the above mentioned prior art, and as shown in FIGS. 9 and 10, the top plate 1 has a top operating unit 2 provided in a widthwise intermediate region of the foreside thereof, and this top operating unit 2 includes a plurality of operating pads 3 to 8 provided in the top plate so that the user can manipulate. On the side of the housing 9, an operating circuit unit 10 is provided, which is connected with the top operating area 2 when the top plate 1 is mounted on the housing 9. The operating circuit unit 10 is provided with a display unit for providing a visual indication of an operating condition of one of the heating regions. Heating elements (heating unit) 11 such as, for example, a radiant heater and one or more induction heating coils aligned with the heating regions are disposed within the housing 9 and beneath the top plate 1. Each of the heating elements 11 is connected with an inverter unit 13 that is controlled by a control unit 12. When one of the heating elements 11 is an induction heating coil, a high frequency electric power of a frequency within the range of 20 kHz to 100 kHz is supplied thereto from the inverter unit 13. When the induction heating coil is to be used, the induction heating coil 11 comes to be positioned below a pan 14 with the top plate 1 intervening therebetween and, therefore, the heating regions and the operating region can be defined on the same plane. For this reason, the heating appliance for cooking can be obtained, in which the risk of operating it erroneously is minimized and the operability, such as, for example, ease of cleaning the top plate surface, is increased. The operating circuit unit 10 is connected with the control unit 12 so that a signal generated as a result of manipulation by the user can be applied to the control unit 12. Also, a display signal indicative of an operating condition of the heating region is applied from the control unit 12 to a display device in the operating circuit unit 10.
Each of the heating regions in the top plate 1 is provided with a temperature sensor 15 for detecting the temperature of the pan 14 and a pan detector 16 for detecting the presence or absence of the pan 14 on the respective heating region, both of which are connected with the control unit 12. The control unit 12 and the inverter unit 13 are connected with an alternating current power source of, for example, AC 200 volts and are therefore supplied with an alternating current.
Each of the operating pads 3, 4, 5, 6, 7 and 8 is in the form of an electrically conductive film laid on a top surface 1A of the top plate 1. Since each of the operating pads 3 to 8 is an area on which the user lays a finger when the associated heating element 11 (In the illustrated prior art appliance shown in FIGS. 9 and 10, two heating elements 11 are employed, but only one is shown in FIG. 9 since FIG. 9 is a transverse sectional view of the appliance.) is desired to be activated, each operating pad 3 to 8 is referred to as “an operating region”. Those operating pads 3 to 8 are formed each by an electrically conductive film such as, for example, a painted or screen printed film of an electrically conductive inking material or paint, or a vapor deposited film of a metallic material and are printed with triangle and round markings and legends “ON” and “OFF” by the use of inking materials or paints of different colors. The operating pads 3 to 5 are associated with the left heating region to switch the corresponding heating coil on or off and also to adjust the heating capacity, whereas the operating pads 6 to 8 are associated with the right heating region to switch the corresponding heating coil on or off and also to adjust the heating capacity. The operating pads 4 and 7 are power switches used to initiate or terminate heating in the respective heating regions. The top plate 1 has a transparent region 17 made up of transparent areas 17 including two semicircular and four bar-shaped areas, which surround the operating pads 3 to 5, and a similar transparent region 18 made up of similar transparent areas 18 which similarly surround the operating pads 6 to 8.
A rectangular transparent region 19 is also provided above the transparent regions 17 and 18, through which the heating power can be indicated by means of light emitting diodes (LEDs).
Connectors 20 to 25 are connected with detecting units 26 to 31 through respective connecting conductors 20A to 25A. The detecting units 26 to 31, the connecting conductors 20A to 25A and the connectors 20 to 25 are each in the form of an electrically conductive film formed in an undersurface 1B of the top plate 1 by the use of a painting or screen printing technique of an electrically conductive paint or a metal vapor deposition technique.
The operating pads 3 to 8 are provided with backlighting units 32 and 33 positioned therebelow for projecting illuminating rays of light upwardly. When the housing 9 is combined together with the top plate 1, the backlighting unit 32 overlaps the transparent region 17 and the backlighting unit 33 overlaps the transparent region 18. Accordingly, one or both of the backlighting units 32 and 33 associated with the left and right heating regions, respectively, can be illuminated when one or both of the backlighting units 32 and 33 is/are energized, to thereby inform the user that such heating region or regions is/are in an “operable condition”.
It has, however, been found that since in the prior art system discussed above, one or both of peripheral areas of the top plate 1 around the operating pads 3 to 8 is/are illuminated by the corresponding backlighting units 32 and 33 to inform the user that one or both of the heating regions is/are in an “operable condition”, one or both of the illuminated transparent regions 17 and 18 is/are highly noticeable enough to provide a considerable difference in brightness between them and respective faces of the operating pads 3 to 8 which are not lighted. This difference in brightness makes the user feel difficulty in noticing legends such as, for example, ON and OFF appearing on the faces of the operating pads 3 to 8. In addition, in view of the fact that the connecting conductors 20A to 25A for connecting the connectors 20 to 25 with the associated detecting units 26 to 31 are so laid as to traverse the transparent regions 17 and 18, the transparent regions 17 and 18 then illuminated are so segmentalized as to permit the transparent regions 17 and 18 to be awkwardly noticed and, hence, the prior art appliance lacks an appealing feature in design.